This application addresses two Broad Challenge areas (15) Translational Science, including specific Challenge Topics 15-NS-104 (Early-stage therapy development) and 15-NS-103 (Demonstration of "proof-of-concept") and Broad Challenge area (08) Genomics, specific Challenge Topic 03-NS-101 (Cross-disease research to identify mechanisms common to Mendelian disorders of low incidence and genetically complex, high incidence disorders). Amyotrophic lateral sclerosis (ALS) is an adult-onset neurodegenerative disorder in which premature loss of upper and lower motor neurons leads to fatal paralysis with a typical disease course of one to five years. While most efforts to understand ALS pathogenesis over the last 15 years have focused on disease caused by mutation in the ubiquitously expressed superoxide dismutase (representing ~2% of all instances of ALS), during the past 14 months, a paradigm shift in understanding ALS has been initiated by discovery that mutations in two strikingly similar DNA/RNA binding proteins, TAR DNA-binding protein (TDP-43) and Fused in sarcoma (FUS/TLS), are also primary causes of ALS. In the normal context, both proteins have been linked to RNA transcription and alternative RNA splicing (FUS/TLS is an integral component of the spliceosome). This has raised the provocative possibility that alterations of RNA metabolism, especially errors of alternative RNA splicing, play a crucial role in ALS pathogenesis. With the further realization that TDP-43-containing cytoplasmic inclusions are found in the vast majority of ALS sporadic patients and in several other neurodegenerative diseases including Frontal Temporal Dementia (FTD), errors in TDP-43 may be central to understanding disease mechanism not just in ALS by also other neurodegenerative disorders. Here, we propose 1) to combine transgenic and gene- targeting approaches to develop new mouse models for TDP-43 and FUS/TLS mediated ALS and 2) to utilize newly developed methodologies linked to high-throughput sequencing to determine the role of TDP-43 and FUS/TLS in the regulation of RNA metabolism as a means to understand how their alterations underlie pathogenesis and to identify new targets for therapy development. PUBLIC HEALTH RELEVANCE: Over the last 14 months, a paradigm shift in understanding what goes wrong in the fatal motor neuron disease Amyotrophic Lateral Sclerosis has been initiated by the discoveries that mutations in a pair of RNA binding proteins (TDP-43 and FUS/TLS) are primary causes of the disease. Through construction and analysis of mice that are genetic mimics of these instances of inherited ALS, how these mutations cause premature death of the motor neurons will be identified. New, very high through put DNA/RNA sequencing methods will be used to identify genes whose expression is altered by the mutations, thereby identifying new targets and approaches for devising a successful therapy for ALS.